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Faster zooming and PictBridge compatibility are among the minor improvements that make the Optio 555 a bit better than its predecessor, the Optio 550. The 555 also shed a few ounces, so it's attractive to amateur photographers who want features such as TIFF-file output, a 5X zoom lens, and manual controls in a relatively compact package. The Optio design doesn't wow us now as it did when the 550 initially shipped, and much of the camera's feature set has become more commonplace, but the 555 remains a solid 5-megapixel amateur model. In its design, the Optio 555 is the Optio 550 with some minor cosmetic changes. These include a different order for the mode dial's icons and a new faceplate for the body, which is now silver and constructed of an aluminum alloy. Otherwise, the 555 is the same as its predecessor: a solid, jacket-pocketable, 7.2-ounce compact with easily accessible controls.

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You can save a group of settings to the mode dial's User selection.

Although you can relax and let the camera's autofocus and autoexposure do their thing, manual operation is just a button-press away. For example, pushing the focus-mode key a few times gets you to its manual setting, which you adjust with the up and down arrows. A focus scale on the left side of the LCD shows the approximate distance. In any shooting mode, the left and right arrows control exposure compensation. Another button cycles between self-timer, burst, time-lapse (interval), and movie modes. A final key toggles between playback and shooting.

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The 555 sports a fairly standard control layout.

Though the menu system is easy to navigate, we don't like having to use it to change settings such as resolution, compression quality, white balance, and ISO speed. Some people might also find the text a bit small. On the upside, you can save a group of options to the mode dial's User selection.

We really dislike the design of the battery/media compartment. Its location on the bottom of the camera makes changing the SD card or the battery impossible during tripod use. Worse, the cell fits in perfectly even if you accidentally insert it backward, leaving you to wonder why the 555 won't power up. This model retains the same amateur-oriented feature set that we liked in its predecessor. The 555's 37.5mm-to-187.5mm, f/2.8-to-f/4.6 zoom lens, like the 550's, sacrifices a bit of wide-angle coverage to provide a useful telephoto setting. Along with a variety of scene modes, the camera offers program, aperture-priority, shutter-priority, and manual modes; a choice of multisegment, center-weighted, and spot light metering; and user control over contrast, sharpening, and color saturation.

Advanced photographers and wannabes will enjoy playing with the 555's special effects and creative shooting modes. For example, a panorama-assist feature works with the included ACDSee software (Windows only) to stitch together your images. You choose at which edge pictures should join with each other, then snap your sequence. On the appropriate side of the LCD, you'll get a transparent view of your last shot's connecting border so that you can properly overlap it with the following frame. And with its fun Stereo 3D mode and bundled stereo-photo viewer, the 555 mimics an old-fashioned &siteid=7&edid=&lop=txt&destcat=ex&destUrl=http%3A%2F%2Fwww%2Ebitwise%2Enet%2F%7Eken%2Dbill%2Fstereo%2Ehtm" target="_new">stereopticon: you capture stereo pairs, print them, then look at them with the viewer. If you have a steady hand and use the LCD's guide grid, you can produce good stereo images without a tripod.

The 555 provides black-and-white, sepia, red, pink, purple, blue, green, yellow, soft-focus, and brightness in-camera filters, which you can apply even after you've taken a picture--a nice touch. You can also crop and resize; replacing the original with the processed shot can squeeze a few extra photos into overloaded storage space. Your first upgrade for this camera will likely be higher-capacity SD media. The included 16MB card can hold only four highest-quality JPEG images and no uncompressed TIFF files. Pentax claims that the 555 operates more quickly than its predecessor, but most of the improvement is in the zoom lens, which has a faster motor. The pause between bootup and the first picture is still more than 5 seconds. Shutter delay, at about 0.9 second, is better than average but still too long to be useful for fast-moving subjects, such as sports. And the short lag is canceled out by the time the camera takes to save shots to the SD card: after each best-quality JPEG image, expect to wait 2.6 to 3.7 seconds, depending on whether you used the flash. As with most high-res cameras, bring along some reading material if you plan to snap TIFF photos; the write time for each of ours was up to 31 seconds.

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The bundled 1,800mAh lithium-ion battery held up well, giving us almost 600 photos, half of them taken with the flash.

In burst mode, we were able to take only four photos in about three seconds before the camera paused to move images from the buffer to the memory card. That's a maximum continuous-shooting rate of just 1.4 frames per second.

Battery life proved to be one of the 555's more endearing performance characteristics. After we'd shot for a week with the 1,800mAh rechargeable lithium-ion cell, we began to wonder if the camera used a perpetual power source. We then switched to a formal testing regimen, exercising such power-hungry features as the zoom lens and the LCD. One full charge gave us almost 600 5-megapixel photos, half of them taken with the flash. That's pretty good.

The LCD shows 100 percent of the scene, but the optical viewfinder provides only 86 percent. Both indoors and in bright sunlight, the screen worked well. Expect to use it for extreme close-ups; the viewfinder's insufficient parallax adjustment makes it easy to lop off an image's top and left sides. When it comes to image quality, the 555 improves a bit on the 550, delivering pleasing though unremarkable pictures for its class. Overall, metering and exposure looked very good. Our flash shots came out a bit underexposed, but only picky photographers would consider them unacceptable. The camera usually blew out highlights but exhibited fine dynamic range in the midtones and the shadows.

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The keys rattle when you type.

Under tungsten lights, with and without the flash, the automatic white balance gave pictures a strong red cast. The preset option produced much better images that fell on the cool side. And the manual white balance worked very well, generating neutral, natural colors.

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Though our pictures were acceptably sharp, the 555 didn't always focus as perfectly as we'd like.

Pentax seems to have reduced its destructive postprocessing. The 555 produced fewer artifacts than the 550 and suffered from none of the older model's vignetting problems. We did see a bit of purple fringing but no more than average. At the camera's best sensitivity setting, ISO 64, there was some noise in dark areas, but overall, images stayed usably noise-free at ISO 64 and ISO 100.